a,b=map(int,input().split())
c=a*b*5
c/=10
if c//1==c:
    print('s='+str(int(c)))
else:
    print('s='+str(c))

a=list(map(int,input().split())) b=a[0]*a[1]/2 if b%1==0: print("s="+str(int(b))) else: print("s="+str(b))

#include<bits/stdc++.h>
using namespace std;
int main(){
    float a,b,s;
    cin>>a>>b;
    s=a*b*5;
    s=s/10;
    cout<<"s="<<s<<endl;
    return 0;
}

#include<bits/stdc++.h>
using namespace std;
int main(){
    int a,b,s;
    cin>>a>>b;
    s=a*b*5;
    s=s/10;
    cout<<"s="<<s<<endl;
    return 0;
}